This invention relates to a combinatorial weighing method and apparatus therefor and, more particularly, to such method and apparatus wherein, if certain conditions are satisfied, two or more appropriate combinations of weighing machines are obtained by just one supply and weighing cycle, followed by discharging articles from each combination of weighing machines in successive fashion.
A combinatorial weighing appartus has a plurality of weighing machines each consisting of a weighing hopper and a weight sensor associated with the weighing hopper. According to a known combinatorial weighing method and apparatus therefor, combinatorial weighing is carried out by weighing articles which have been introduced into the weighing hoppers of the weighing machines, selecting the combination of weighing machines (referred to as the "optimum" combination) that gives a total weight value equal to a target value or closest to the target value within preset allowable limits, discharging only those articles contained by the weighing hoppers of the selected weighing machines, and subsequently replenishing the emptied weighing hoppers with new articles to prepare for the next weighing cycle. The foregoing sequence of steps is repeated to carry out a continuous, highly accurate weighing operation automatically.
FIG. 1 illustrates, in diagrammatic form, the mechanism of a combinatorial weighing appartus for practicing the above-described weighing method. Numeral 1 denotes a main feeder of vibratory conveyance type. Articles to be weighed are introduced into the main feeder 1 and imparted with vibratory motion for a predetermined length of time so as to be dispersed radially outward from the center of the main feeder. Numerals 2, 2 . . . denote n-number of weighing stations which are arranged around the main feeder 1 along radially extending lines to receive the articles dispersed by the main feeder. Each weighing station 2 includes a dispersing feeder 2a, a pool hopper 2b, a pool hopper gate 2c, a weighing hopper 2d, a weight sensor 2e, and a weighing hopper gate 2f. The dispersing feeder 2a comprises an independently vibratable conveyance device for feeding the articles by means of vibration, or an independently operable shutter. In either case, each dispersing feeder 2a is so arranged that the articles received from the centrally located main feeder 1 can be introduced into the corresponding pool hopper 2b disposed therebelow. The pool hopper gate 2c is provided on each pool hopper 2b in such a manner that the articles received in the pool hopper 2b are released into the weighing hopper 2d when the pool hopper gate 2c is opened. Each weighing machine is composed of a weighing hopper 2d and a weight sensor 2e attached thereto. The weight sensor 2e is operable to measure the weight of the articles introduced into the weighing hopper 2d of the weighing machine, and to apply an electrical signal indicative of the measured weight to a combination control unit, not shown. The combination control unit then selects the combination of articles (the "optimum" combination) which gives a total weight equal to a target value or closest to the target value within preset allowable limits. Each weighing hopper 2d is provided with its own weighing hopper gate 2f. Upon receiving the signals from each of the weight sensors, a drive controller, not shown, produces a signal to open only the weighing hopper gates 2f of those weighing hoppers 2d that give the optimum combination, these gates 2f discharge the articles from the corresponding weighing hoppers 2d in a common chute 3 where they are collected together. The collecting chute 3 has the shape of a funnel and is so arranged as to receive the articles from any of the circularly arrayed weighing hoppers 2d via the hopper gates 2f, which are located above the funnel and substantially along its outer rim. The articles received by the collecting chute 3 are collected at the centrally located lower end thereof by falling under their own weight or by being forcibly shifted along the inclined wall of the funnel by a mechanical scraper or the like, which is not shown. The collecting chute 3 is provided with a timing hopper 4 at the lower end thereof, for temporarily holding the collected articles. The arrival of an externally applied release signal from a packaging machine or the like causes the timing hopper 4 to release the retained articles from the system.
The foregoing combinatorial weighing apparatus is an extremely useful machine for obtaining the optimum combination of articles having a total combined weight equal to the target value or closest to the target value within the preset allowable limits. The obtained combination of articles is discharged from the apparatus.
There are instances where the target value used in the combinatorial computations is not fixed, even for articles of the same type. The reason is that it is sometimes necessary to change the target value setting depending upon the particular production schedule. For example, though the main product in a production line may be 100 g bags of potato chips, there are cases where it is necessary to produce, say, 200 and 500 g bags of potato chips. This means that combinatorial weighing would have to be performed based on target weight values of 100 g, 200 g and 500 g, respectively. In order to execute combinatorial weighing for a plurality of target values by means of a single combinatorial weighing apparatus, a method which will now be described has been developed and put into use in the prior art. In explaining this conventional method, we will assume that 100 g, 200 g and 500 g bags are to be produced, and that the processing must be carried out at a rate of 120, 60 and 24 weighing cycles per minute, respectively. The method is as follows:
(1) Means are taken to achieve high-speed weighing so that the combinatorial weighing apparatus can perform combinatorial weighing at a rate of up to 120 weighing cycles per minute. To this end, two combinations each giving a total combined weight within the preset allowable limits are obtained for each article supply and weight measurement cycle, and the articles are discharged from the weighing machines belonging to each combination. By obtaining two combinations for each single supply and weight measurement cycle in this manner, the time required for weight measurement is reduced. That is, since weighing machines tend to oscillate when supplied with articles, a weight measurement cannot begin until enough time needed for the weighing machines to stabilize has passed. When just one combination is obtained per cycle, the waiting time of a prescribed duration is required between each and every combination in order for the weighing machines to stabilize. By obtaining two combinations per cycle, therefore, the waiting time is required only between every two combinations.
(2) Whenever a target value setting is changed, the amount of articles supplied to each weighing machine is adjusted to obtain the highest weighing accuracy. To accomplish this, the number of weighing machines selected as the optimum combination for the purpose of discharging their articles is rendered virtually constant irrespective of the target value. The adjustment of the amount of articles supplied to the weighing machines requires that the weighing accuracy be checked so that fine adjustments can be made.
(3) The combinatorial weighing apparatus must have a rigid construction strength and hopper capacity, capable of weighing out 500 g of articles. At the same time, the apparatus must be capable of weighing out 100 g of the articles. To these ends, a weighing computing mechanism must be adapted to provide two sets of results with just one article supply operation.
According to the prior art, therefore, the change in target value is dealt with by designing a combinatorial weighing apparatus in accordance with items (1) to (3). However, with the conventional method, the amount of articles supplied to each of the weighing hoppers must be adjusted in accordance with the change in target value, so that a rapid changeover from one target value to another cannot take place. In addition, when a weighing hopper designed to handle a larger volume of articles is used for articles occupying only a small volume, the articles are required to fall a greater distance because of the larger dimensions involved. This causes the articles to sustain damage upon impact when they are released from the hopper. Furthermore, in order to execute combinatorial processing at a rate of 120 weighing operations per minute when weighing out large volumes of articles, the production rate of the overall system must be raised a stroke, or else the supply of articles from an earlier stage of the production line will not be able to keep pace, thereby resulting in a shortfall of the articles supplied. Conversely, when weighing out articles in small volumes, there is a tendency for articles to be supplied in an overabundance from the earlier stage of the production line.